The present invention encompasses articles and methods for providing softening and anti-static benefits to fabrics in an automatic laundry dryer. More specifically, damp fabrics are commingled with particular "sorbitan esters" in an automatic clothes dryer and are provided with a soft, anti-static finish concurrently with the drying operation. The softening and anti-static sorbitan esters herein are preferably employed in combination with a dispensing means adapted for use in an automatic dryer.
Treatment in an automatic clothes dryer has been shown to be an effective means for imparting desirable tactile properties to fabrics. For example, it is becoming common to soften fabrics in an automatic clothes dryer rather than during the rinse cycle of a laundering operation. (See Gaiser; U.S. Pat. No. 3,442,692; issued May 6, 1969)
Fabric "softness" is an expression well-defined in the art and is usually understood to be that quality of the treated fabric whereby its handle or texture is smooth, pliable and fluffy to the touch. Various chemical compounds have long been known to possess the ability to soften fabrics when applied to them during a laundering operation.
Fabric softness also connotes the absence of static "cling" in the fabrics, and the commonly used cationic fabric softeners provide both softening and anti-static benefits when applied to fabrics. Indeed, with fabrics such as nylon and polyester, the user is more able to perceive and appreciate an anti-static benefit than a true softening benefit.
Fatty alkyl cationic anti-static softening compounds and compositions designed for application to fabrics in an automatic dryer have been the subject of recent innovations (See, for example, Furgal, U.S. Pat. No. 3,634,947, issued Jan. 18, 1972 and Morton, U.S. Pat. No. 3,686,025, issued Aug. 22, 1972.). Other fatty materials have been suggested for use as dryer-added fabric softeners. (See, for example, Hewitt et al, U.S. Pat. No. 3,676,199, issued July 11, 1972 and the co-pending application of Murphy and Habermehl, Ser. No. 417,329, filed Nov. 19, 1973.). Included among these prior softening compositions are various glycerides in combination with oil-soluble, lower-ethoxylated surfactants. Triglyceride fabric treating agents are disclosed in Bernholz et al, U.S. Pat. No. 3,785,973, issued Jan. 15, 1974.
As pointed out in Hewitt et al, U.S. Pat. No. 3,676,199, issued July 11, 1972 and Wixon, U.S. Pat. No. 3,766,062, issued Oct. 16, 1973, many of the prior art softening agents stain or discolor the conditioned fabrics when used in an automatic dryer. The unfortunate tendency of such materials to stain fabrics is apparently caused by the presence of the fatty alkyl groups in the active softening compounds. Unevenly distributed fatty softeners can appear as blotchy, oily stains on the treated fabrics. Thus, the chemical structure which gives rise to the soft, lubricious feel associated with the prior art softeners also causes them to be potential fabric stainers.
Heretofore, a variety of mechanical methods have been employed in an attempt to reduce the tendency of dryer-added softeners to stain fabrics. The prior art fabric softening agents have been sorbed onto flexible articles designed to provide controlled release at dryer operating temperatures. While such articles are quite attractive from the standpoint of ease of manufacture and economics, staining can still be a problem if an improperly formulated flexible article becomes entangled in clothing. Various rigid dispensers and appliances have been designed which assertedly avoid any exceptionally high concentrations of softening agent being undesirably deposited on the fabrics in the form of greasy stains (See Hoeflin, U.S. Pat. No. 3,633,538, issued Jan. 11, 1972 and Grand et al, U.S. Pat. No. 3,698,095, issued Oct. 17, 1972). However, such dispensers are costly and have not come into general use.
Certain surfactants have been suggested for obviating the tendency of the prior art softeners to stain fabrics. (See the co-pending application of Murphy and Habermehl, Ser. No. 440,932, filed Feb. 8, 1974.) This non-staining aspect is especially important when the common polyester fabrics, which are oleophilic and particularly susceptible to oily staining, are softened in an automatic dryer.
As noted above, many softening compounds have been adapted for use in automatic dryers by fashioning articles which contain a pre-measured amount of the softener. Preferred articles comprise a flexible sheet substrate coated and/or impregnated with an optimal, pre-measured amount of a fabric softener. These articles are simply added to a dryer together with the fabrics to be dried. The heat and tumbling action of the dryer helps to dispense the softener onto the fabric surfaces (See, for example, Perez-Zamora, U.S. Pat. No. 3,632,396, issued Jan. 4, 1972). However, once sorbed onto the sheet substrate, some softeners tend to remain affixed thereto, rather than being dispensed onto the fabrics. Thus, the user of such articles cannot be assured that the optimal amount of softener originally present in the article is, in fact, deposited on the fabrics. To obviate this problem, it has been suggested to layer the softener onto the sheet together with surfactant-type release agents which insure substantially complete transfer to the fabrics (See Perez-Zamora, U.S. Pat. No. 3,632,396, issued Jan. 4, 1972).
Finally, some cationic materials recognized for use as fabric softeners and anti-static agents in dilute, aqueous rinse baths are not particularly useful in certain automatic dryers in that they are reported to soften and loosen certain paints used to protect the dryer drum, and to corrode exposed metal surfaces of some automatic dryer drums.
It has now been found that fatty esters of certain poly-ols, especially the so-called "sorbitan esters", are particularly useful as dryer-added fabric softeners. Such materials contain several free or esterified hydroxyl groups.
Various compounds containing hydroxyl groups are recognized as useful fabric scrooping agents in aqueous media, e.g., those listed in Speel et al, Textile Chemicals and Auxiliaries, 2nd Edition, Reinhold Publishing Corp., 1957. Some ethoxylated alcohols are further known to be useful in textile lubricating compositions (See Cohen et al, U.S. Pat. No. 3,773,463, issued Nov. 20, 1973.
The use of various sorbitan ester compounds or derivatives to treat fabrics other than in an automatic clothes dryer is known (See Atlas Powder Company Bulletin -9, "Industrial Emulsions with Atlas Surfactants", 1953; Eisen, U.S. Pat. No. 2,461,043, issued Feb. 8, 1949; Simon et al, U.S. Pat. No. 2,665,443, issued Jan. 12, 1954; Karg, U.S. Pat. No. 3,652,419, issued Mar. 28, 1972 and Crossfield, U.S. Pat. No. 3,827,114, issued Aug. 6, 1974). Softening compositions for use in aqueous media comprising (among other components) a quaternary ammonium compound and a sorbitan ester are disclosed in Okazaki et al, U.S. Pat. No. 3,793,196, issued Feb. 19, 1974 and Waitkus, U.S. Pat. No. 2,735,790, issued Feb. 21, 1956.
The U.S. patent application of Zaki, Ser. No. 461,312, filed Apr. 16, 1974, now abandoned in favor of copending continuation-in-part application having Ser. No. 543,607, filed Jan. 23, 1975 discloses fabric softening articles comprising a major amount of a cationic softener and a minor amount of a sorbitan ester material as an auxiliary softener and release aid.
The above prior art references relating to sorbitan esters are, for the most part, directed to the aqueous media treatment of yarn during textile processing. Such references do not appear to recognize the particular advantages of these materials as softening agents for use in automatic laundry dryers.
It has now been found that sorbitan esters are especially useful in automatic dryers relative to other prior art fabric softeners. More specifically, the sorbitan esters used herein help alleviate all the aforesaid problems relating to through-the-dryer fabric softening.
First, the sorbitan esters impart a soft, lubricious feel to fabrics when applied to such fabrics in a heated clothes dryer.
Second the sorbitan esters provide an anti-static effect. Accordingly, it is not necessary to use additives with sorbitan esters to achieve the dual benefits of fabric softening and reduced static charge.
Third, the sorbitan esters can be readily dispensed onto fabrics from dryer-added flexible substrate articles by the heat and tumbling action of the dryer without the need for adjuvant release agents.
Fourth, the sorbitan esters provide minimal staining of fabrics when used in the manner disclosed herein.
Finally, the sorbitan esters are safe for use in contact with dryer drum paint and/or metal dryer drum surfaces and, in fact, function as a corrosion inhibitor in the dryer.
It is an object of this invention to provide a safe, effective means for softening fabrics in a clothes dryer.
It is another object herein to provide a superior article of manufacture adapted for imparting softness and anti-static benefits to fabrics in a clothes dryer.
It is another object herein to provide articles of manufacture and methods for softening fabrics in a laundry dryer by employing materials which do not disadvantageously interact with dryer drum metal or paint.
These and other objects are obtained herein as will be seen from the following disclosure.